Vaporization of liquefied gases



Oct. 16, 1962 L. E. PUTMAN VAPORIZATION OF LIQUEFIED GASES 4 Sheets-Sheet 1 Filed March 31, 1958 FIG.2

FIC-5.3

Oct' 16, 1962 L. E. PUTMAN 3,058,317

VAPORIZATION 0F LIQUEFIED GASES Oct. 16, 1962 L. E. PUTMAN 3,058,317

VAPORIZATION OF LIQUEFIED GASESv Oct. 16v, 1962 l.. E. PUTMAN 3,058,317

VAPORIZATION 0F LIQUEFIED GASES Filed March 31, 1958 4 Sheets-Sheet 4 3,658,317 VAIGRIZAHON F MQUEFMD GASES Laurel E. Putman, Livingston, NJ., assigner to Superior Arr Products Co., Newark, NJ., a corporation of Delaware Filed Mar. 3l, i958, Ser. No. 725,3@ 14 laims. (Cl. 62-52) The present invention relates to the vaporization of liquefied -gases and more particularly to the vaporization of liquefied gases having boiling points below the temperature of a gaseous heat source.

The invention is particularly concerned with the vaporization of liquid oxygen, liquid nitrogen and liquid argon by heat-exchange with atmospheric air at ambient temperature and will therefore be described principally in connection with these gases. However, the principles of the invention are in general applicable to the vaporization of any liquefied gas by means of heat-exchange with an impure gas whose temperature is greater than the boiling point of the liquefied gas.

At the present time, most commercial installations for the vaporization of liquefied oxygen, nitrogen or argon employ relatively expensive and complicated methods such as passing the gas through tubes which are externally heated by water or some other medium which is in turn heated by steam or electricity. The power consumption of such heating methods is expensive and the apparatus is complicated.

Attempts have been made to utilize ambient air as a source of heat, but such attempts have either not been successful or have been ineiiicient with regard to operating costs, plant required, or both. The principal diiiiculty encountered in the use of ambient air has been the fact that atmospheric air always includes water vapor, carbon dioxide and other gases which, upon contact with the cold surface of the vaporizer and heating coil, rapidly condense out, due to the extreme temperature differences, and the film of condensation so formed, acts as an insulation. Over a period of time the film progresses in thickness and direction to the point where the heat-exchanger surface for all practical purposes becomes non-effective. More or less practical solutions of this problem have been suggested, one of which is to provide a series of two or more vaporizer and warming coils, which can be alternately used, with the intent that While the condensible lm is building up on a new surface, the condensed film on the previously used surface will evaporate due to static ambient conditions. This is not practical in temperatures below 5 C. since water vapor which is the primary constituent of the condensed film will not evaporate in sufiicient time to allow the use of other than extremely large surfaces in multiples which may be prohibitive from the space or economic standpoint. One variation uses auxiliary methods for removing the relatively poor conductive -lms of condensed gases, such as electric heating by direct conduction, or indirectly heating the surface by heating the ambient air. Such expedients are, of course, expensive and undesirable.

Another attempt to solve the problem has been to provide a heat-exchanger surface with liquid oxygen flowing internally and atmospheric air externally at high volumes and high velocity so that the temperature of the air does not fall below 5 C. Such a method is described in Monroe and Freud Patent 2,729,074 granted January 3, 1956. Even under such conditions condensation of Water takes place and provisions have to be made to ensure that the temperature of the ambient air does not fall below its freezing point at atmospheric pressure. Such provisions include heating of the air, directly or indirectly.

The principal object of the present invention has been are to provide a novel and improved method for vaporizing a liquefied gas.

More particularly it has been a principal object of the invention to provide a novel and improved method for vaporizing a liquefied gas through indirect heat-exchange with a warmer gas, which method is efficient both as to operating costs and plant requirements.

Another object of the invention has been to provide a novel and improved method for vaporizing liquefied oxygen, nitrogen or argon through indirect heat-exchange with ambient air.

Gther and further objects, features and advantages of the invention will appear more fully from the following description.

In the practice of the invention, a liquefied gas, c g., oxygen, nitrogen, or argon, is passed through a heat-exchanging device wherein indirect heat-exchange with a stream of ambient atmospheric air is afforded. The process conditions are selected so that condensible gases in the ambient air are deposited on a portion of the heatexchanger surface during a first part of the heat-exchanging cycle and are deposited on a second portion of the heat-exchanger surface during a second portion of the cycle. During the rst part of the cycle, condensed gases are removed from the second portion of the heat-exchanger surface by action of the air flow while during the second part of the cycle condensed gases are removed from the first portion of the heat-exchanger surface by action of the air iiow. In this way the net effective heatexchanger surface is maintained substantially constant irrespective of the ambient air temperatures and the concentrations of condensible gases in the ambient air. It is highly desirable that the invention be carried out so that co-current flow is maintained during both parts of the heat-exchanging cycle since with such flow operation can be maintained regardless of ambient condition and over the largest range of condensible gas in the ambient atmosphere. As used herein, the term condensible gases is intended to include also condensible vapors such as water vapor. As explained previously, the process of the invention is applicable to any liquefied gas, for example methane, and to any source of ambient atmosphere having a temperature greater than that of the boiling point of the liquefied gas, provided of course, that the condensible gas concentration in the ambient atmosphere represents only a small portion of the total ambient atmospheric ow.

rIhe invention will now be described in greater detail with reference to the appended drawings, in which:

FIG. l is a schematic illustration of one form of heatexchanger system for carrying out a preferred method in accordance with the invention;

FIG. 2 is a schematic illustration of another form of heat-exchanger system for carrying out a modified method in accordance with the invention;

FIG. 3 is a schematic illustration of still another form of heat-exchanger system for carrying out a further modification of the invention;

FIG. 4 is a schematic illustration of another form of heat-exchanger system for carrying out another modification of the invention;

FIG. 5 is a schematic illustration of another form of heat-exchanger system for carrying out still another modification of the invention;

FIG. `6 is a side elevational view of a practical form of apparatus for practicing the invention; and

FIG. 7 is an end view of the apparatus shown in FIG. 6.

Referring now to the drawings, and more particularly to FIG. l, the heat-exchanger apparatus, which may be termed a vaporizer-warmer, is illustrated in the form of a coil lll through which flows liquefied gas from a source 11, which might be, for example, a tank. Lique- 3 fied gas from the source 11 flows to the coil 10 through a feed line 12, a four-way valve 13 and another feed line 14. A pump 12' may be inserted in the feed line 12 to build up the liquefied gas to any desired pressure. With the four-way valve 13 in the position shown, the liquefied gas will .be delivered to the left end of the coil 10, which is designated as point 15. The right end of the coil- 10, which is designated as point 16, is connected to four- Way valve 13 through a line 17. With the four-way valve 13 in the position shown, the line 17 is connected through the valve to a discharge line 18.

The liquefied gas from the source 11 may be at highor low pressure as desired. In general, the higher the pressure of the liqueed gas source the more advantageous it will be for the liquefied gas to flow internally of the heat-exchanger coil 10, although the choice of internal or external flow will also depend an other factors such as economy, ease of maintenanceand similar criteria. The pump 12' may be used to provide a suitable high pressure,

Ambient atmosphere at any desired pressure is forced by suitable means, such as a fan 19, over lthe vaporizer- Warmer coil 10. A shroud or housing 2G, open at the ends, is disposed about the coil and serve to direct and control the ambient flow over the coil 10. The open left end of the shroud 20 is designated 21, While the open right end of the shroud 20 is designated 22. The ambient atmosphere, which will generally be atmospheric air, enters the shroud 20 at point 22, contacts the coil 10 at point 16, loses contact With the coil 1() at point 15, and exits from the shroud 20 at point 21, or vice versa depending upon the direction of rotation of the motor driving the fan 19.

In this, the preferred form `of the invention, co-current 22. rAt the same time, liquefied gas is delivered to the coil 10 at point 15 and the warmed and vaporized gas exits from the coil 10 at point 16. Since the temperature of the liqueed gas will be lowest at the point of delivery to the vaporizer-warmer coil, the temperature difference between ambient air and liqueed gas will be greatest at point 15. This temperature difference is so large that the condensible gases in the ambient air freeze out on the exchanger surface, starting at point 15. As the condensate Ibuilds up on the exchanger surface adjacent the point 15, the transfer of heat between the liquefied gas and the ambient air at this point Will become less efiicient, resulting in the zone of freeze-out extending in the direction of point 16.

After a period of time, which can be predetermined, the exchanger surface will be covered with a sufficient thickness of condensate to prevent the portion of the exchanger surface between the point 15 and the middle of the coil 10 from functioning as an effective heat-exchanger surface, so that the major portion of the Vaporizing and Warming of the liquefied gas will then occur in that of .the coil 10 nearest the point 16. The buildup of condensate is a function of time depending upon such variables las relative flows of lliquefied gas and ambient atmosphere, amount of condensible in the ambient atmosphere, and -total surface are available in the vaporizerwarmer 10. Y

The liquefied gas leaving the vaporizer-warmer 10 and delivered to the line 18, will have been vaporized and heated to within a few degrees of the temperature of the ambient atmosphere.

Ambient atmosphere leaving the shroud at the point 22 will be essentially free of all condensibles since they have been frozen out on the surface of the vaporizer-warmer 10. As the buildup ofcondensibles on the exchanger surfacel proceeds, a point will be reached at which the effective heat-exchanger surface is reduced so far (because of the insulating layer of condensibles) that the vaporized and warmed gas leaving the system at point 16 is at a colder temperature than permissible.

At this time the flow of liquefied gas from the source 11 is directed to the point 16 instead of the point 15 by reversing four-way valver13. Such reversal of the fourway valve 13 will interconnect lines 12 and 17 on the one hand and lines 14 and 18 on the other hand. Thus the liqueed gas enters the vaporizer-warmer at a point which has little or no condensed vapor or gas on its surface, i.e., the righthand portion of the vaporizerwarmer. This righthand portion will be at substantially maximum effectiveness in affording heat-exchange because it has little or no condensed gas or vapor on its surface. At the same time, the direction of flow of air is changed so that the fan 19 directs air through the shroud 2t) from point 22 to point 21, thus maintaining co-current flow.

The liquefied gas delivered at point 16 will be warmed and Vaporized as it passes through the vaporizer-warrner 10 toward point 15. Condensible gas in the ambient air will start freezing out and depositing on the exchanger surface at a point 16 since this is now the point of greatest temperature difference between the liquefied gas and the ambient air. As the layer of condensed gas on the exchanger surface builds up to provide insulation, the point of maximum temperature difference will move toward the left in FIG. l, i.e., toward the point 15.

As the ambient air flows over the right-hand part of the exchanger surface, condensible gases contained therein are deposited on the exchanger surface, as described, so that when this air reaches the left-hand part of the exchanger surface it will have lost at least a major part of its condensible gas content and will certainly be unsaturated. As this unsaturated air passes over the previously deposited condensibles on the left-hand part of the exchanger surface, Le., that part between the center and point 15, the previously deposited condensibles tend to and ldo diffuse `or evaporate into the air, cleaning the heat exchanger surface which had been ycoated during the first portion of the cycle. The second portion of the cycle is, of course, that portion in which both the liquefied gas and the ambient air travel from right to left in FIG. l.

When the buildup of condensibles on the exchanger `Surface reaches a level in which the vaporized gas discharged at the point 15 is at Ia colder temperature than permissible, the four-way valve 13 is reversed again to its original position so that liquefied gas will be delivered to the point 15 and the direction of air ow is also reversed so that air will flow from point 21 to point 22. This initiates the first portion of a new cycle. In this new cycle, ambient air passing over the right hand portion of the exchanger surface will pick up condensibles vfrom this portion of the exchanger surface because the ambient air `will have vlost at least a substantial proportion of its condensible gas content from having first flowed over the lefthand portion of the exchanger surface which is now the coldest portion. The operation is continued with the direction of fiow of the liquefied gas and ambient lair being reversed as necessary.

Since in FIG. l co-current flow is maintained at all times, both portions of the cycle may be of equal duration. In general, the cycle portion times may be selected as -desired provided that each cycle portion is of sufficient duration to permit substantially complete cleaning of condensible gases deposited during the preceding cycle portion. The changeover from one cycle portion to the next may be efected manually or Iautomatically and may be initiated by the passage of a predetermined time, observation of the temperature of the warmed and Vaporized gas, or observation of the condensible buildup on the vaporizer-warmer surface. The use of co-current flows of yapproximately equal masses minimizes the power cost for moving the ambient air 4and also permits the use of a minimum size heat-exchanger surface since the cycle duration can be made quite short. This is of particular importance where equipment should be small in size.

While it is preferable to maintain co-current flow of the liquefied gas and ambient air and this condition should be used to provide the best results and the greatest efficiency, satisfactory results can generally be achieved without maintaining co-current flow. An arrangement in which the direction of flow of the ambient air only is reversed is illustrated in FiG. 2. In FIG. 2, the vaporizer-warmer is divided into two sections 30 and 30. Liqueed gas from a source 31 ows through feed line 32 and feed lines 33 and 33 to the coils 30 and 30. the other ends of the coils 3l) and 3G are connected through delivery lines 34 and 34', respectively, to the vaporized gas discharge line 35. A shroud or housing 36, open at yboth ends, is provided around the coils 3ft and 36 to direct and control the llow of ambient air set up by a fan 37. The fan 37 is reversible so that it can direct ambient air from point 38 to point 39, or from point 39 to point 38. The lefthand end of coil 30 is labeled 4@ While the righthand end thereof is labeled 41. Similarly, the lefthand end of coil 30 is labeled 40' while the righthand end thereof is labeled 41'.

During a first part of each cycle, the fan 37 is caused to direct air from right to left, i.e., from point 39 t0- Ward point 38. Air passing over the coil 3G will contain condensible gas which will freeze out on the coil 30'. This same air will then pass over the coil 30; but since a major portion of its condensible gas content will have been deposited on the coil 30', this air will 'be able to absorb condensibles and hence will be able to clean the surface of the coil 30 of condensible gas deposited thereon during the second part of the preceding cycle. When the condensible gas deposited on the coil 30' exceeds a desired amount so that the temperature of the vaporized gas delivered through the tube 34 is too 10W, the direction of air flow is reversed. This results in cleaning action on the surface of coil 30 and a deposition of condensibles on coil 30'. In other words, while one section of the vaporizer-warmer is having a layer of condensibles built up thereon, the other section is being cleaned by the `air which has been stripped of condensibles by the first section. The `ambient air entering the shroud 36 at 38 or 39, as the case may be, and then passing over the adjacent vaporizer-warmer coil section 30 or 30', is relatively free of condensibles by the time it reaches the other section of the vaporizer-warmer coil 30 -or 30, as the case may be, and will absorb condensibles from the latter.

In the case of FIG. 2, the two portions of the cycle may be of identical durations if the two vaporizer-warmer sections afford equal exchanger surface areas. The time duration of each portion of the cycle will be limited by the length of time required to build up a layer of condensation on either section of the vaporizer-warmer to the point where the vaporized and warmed gas leaving that section becomes too cold due to the condensibles on the coil surface destroying the effectiveness of the heat-transfer surface.

An operation in which the direction of Iair flow only is reversed, as described in connection with FIG. 2, is especially desirable when it is more economical and practicable to maintain -a one-way flow of liquefied gas, such as in a very high-pressure system-cycle control of a very high-pressure fluid being diicult.

Referring now to FIG. 3, there is illustrated an arrangement in which only the direction of flow of the liquefied gas is changed. Liqueiied gas from a source 56 is delivered to the lefthand end |(point 51) of vaporizer-Warmer coil l52 through delivery line 53, a four-way valve `5d and a delivery line 55. The vaporized and warmed gas discharged from the righthand end (point 56) of vaporizer-warmer coil 52 is delivered to discharge line 57 through a line 58 and the four-way valve 54.

By reversing the four-way valve 54, liquefied gas may be delivered to the righthand end of coil 52 and the vaporized and warmed gas may be discharged through the line 55 to the line 57. Ambient air is directed through a shroud or housing 59 and `over the coil 52 by a fan 60. The fan 6i? causes the air to enter the shroud at point 62 and to leave at point 6l.

=In the rst portion of each cycle, liquefied gas enters the vaporizer-warmer 52 at point 51, resulting in a deposit and buildup of condensibles on the exchange surface starting at the point 5l and moving progressively toward the right in FIG. 3. When the buildup of condensibles results in too low a temperature of the vaporized and warmed gas discharged at the point 56 the direction of flow of the liquefied gas is reversed, resulting in a deposition of condensibles at the righthand end of the exchanger Ksurface and a cleaning of the lefthand portion of the exchanger surface.

By properly sizing the exchanger surface area, mass flows and cycle times, the unit shown in FIG. 3 will operate indefinitely. Since the flow is not co-current during both portions of the cycle, care should be taken to maintain a relatively large flow of ambient air in proportion to the lluid being vaporized since during the counter-current ilow portion of the cycle, the removal of condensibles from the frozen portion of the heat exchanger is accomplished by a much less driving force. This is to say that the air owing from 62. to 61 contains a maximum of condensibles when the warmed and vaporzed gas exists at point S6 and the removal of condensibles for the zone nearest point S6 is done only by the difference between degree of concentration possible in ambient air and the degree actually present. During the other portion of the cycle a substantial proportion of the condensibles are frozen out of the air before it passes over the surface to be cleaned, thus making the cleaning easier. It is unlikely that the air available will be saturated with respect to water and carbon dioxide, which are the major condensible constituents, so that, assuming that the air is not saturated with these constituents, the only precaution that should be taken is to Aprovide a relatively longer cycle time for the countercurrent flow. Alternatively, a larger exchanger surface may -be used for the counter-current flow, as by unequal division of the exchanger surface between the two portions of the cycle. Another alternative, but which would be diflicult to control under varying ambient conditions, is to provide a greater flow rate of ambient air during the counter-current ilow than during the co-current ow.

Another exchanger arrangement in which co-current flow can be maintained is illustrated in FIG. 4. In FIG. 4, liquefied gas from a source 70 is supplied to lthe righthand end 71 of a vaporizer-warmer coil section 72 through a feed line 73, a four-way valve 74 and a feed line 75. The liquefied gas discharged at left end 76 of coil 72 is conducted to left end 77 of another vaporizerwarmer coil section 78. The -sections 72 `and 78 are axially spaced within a shroud or housing 79 which serves to direct and control the flow of air from a fan 80 over the exchanger surfaces. The fan St) is powered by a reversible electric motor 81. Vaporized and warmed gas discharged from right end 82 of coil section 78 is delivered to discharge line 83 through a line 84 and fourway valve 74.

During a first portion of each cycle, liquefied gas is conducted from right to left in coil 72 and then from left to right in coil 7S. At this time the fan 80 is powered to force air from left to right in the shroud 79 so that condensibles from the ambient air are deposited on the coil 72 and are removed from the coil 78. A cycle-timing control which m-ay =be operated by a clock mechanisni 85 reverses the four-way valve 74 and also reverses the electric motor 81 so that liquefied gas will liow from right to left in coil section 78 and thence from left to right in coil sections 72 while ambient air will be dil rected from right to left in the shroud 79. During thisV second portion of the cycle, condensibles from the ambient air will be deposited on the coil section 78 and will-be cleaned from the coil section 72.

Another exchanger arrangement in which co-current iiow can be maintained is illustrated in FIG. 5. Referring to FIG. 5, the Vaporizer-warmer is formed by two separate ,coils 90 and 91 which are axially coincident but laterally spaced from each other. In practice, the coils 90 and 91 may be wound close to each other. Liquefied gas from` a source 92 is conducted through a feed line 93 to left end 94 of coil 90 and through a feed line 95 to. right end 96 of coil 91. Vaporized and warmed gas from the right end 97 of coil 90 is delivered through a line 98 and a valve 99 to discharge line 100. Similarly, vaporized and warmed gas from the left end of coil 91 is delivered to the discharge line 100 through a line 101 and a valve 102. The vvalves 99 and 102 are controlled by solenoids 103 and 104, respectively, which are in turn controlled by clock-control mechanism 105. The clock mechanism 105 also controls a reversible electric motor 106 which drives fan 107. The fan 107 forces air. from right to left or left to right within a shroud or housing 108 provided around the vaporiZer-warmer coils 90 and 91.

The valves and solenoids 99-103 and 1412-104 are arranged so that when one valve is open the other is closed, and vice versa. With the valve 99 open, liquefied gas passes through coil 90 from point 94 to point 97. At this time valve 102 is closed so that no iiow occurs through the coil 91. Air passing from left to right through the shroud 108 vaporizes and warms the liquefied gas in the coil 90, deposits condensibles from left to right on the coil 90 and removes condensibles from the coil 91 which had been deposited thereon during the latter portion of the preceding cycle. Similarly, air passing from right to left in the shroud 108 vaporizes and'vwarms the liquefied gas in the coil 91, deposits condensibles on the coil 91 and removes condensibles from the coil 90 which had been deposited thereon during the latter portion of the preceding cycle. It will be observed that when gas and air ow occur from left to right frosting and depositing occury from left to right, and vice versa.

It is particularly desirable that the invention be carriedV out so that during each cycle portion the ambient air first sweeps over the coldest area of the heat-exchanger surface and then over the area to be cleaned. In this way a maximum amount of the moisture in the air will be frozen out on the cold surface and the air will have a: maximum capacity for picking up moisture from the warmer surface due to the concentration difference driving force, which to some extent is independent of temperature.

A practical form of apparatus for carrying out the method of the invention is illustrated in FIGS. 6 and 7. The apparatus of FlG. 6 comprises three principal sections, these being a fan and motor section contained in a housing 110, a heat-exchanger section contained in a housing :111, whichV also serves as the air directing shroud, and' aV liquid inlet-gas outlet manifold 112 mounted on the housing 111. The housings 110 and 111 are provided with flanges 113 and 114, respectively, which may be bolted together with bolts 115.

The housing 110 contains a reversible electric motor and a fan arranged to blow ambient atmospheric air through the housing 111 in either direction, the air passing in the annular space between the housing 111 and a core 116, which may be a hollow cylinder closed at one or bothends. The fan may draw air in through a port 117 at the left end of the housing 110 and exhaust the air through the annular opening 118 at the right end of the housing 111, or draw in air through the opening 118 and exhaust the air through the port 117, depending upon the direction of fan rotation.

A three-section annular heat-exchanger coil 119 is mounted on the core 11G within.v the housing111. The coil is Wound in three sectionstof. different diameter and ywhich are connected together by headers at each end, the headers terminating in fluid connections 120 and 121, respectively. 'Ihe three coil sections are thus connected in parallel so that finid entering at 120 continuously progresses toward the exit at 121, or vice versa. Thus, even though the individual turns of the coil sections are disposed generally perpendicular to the direction of air iiow, the direction of flow of the iiuid contained in the coil is parallel to the direction of air flow. As illustrated, the three layers or sections of the coil 119 are spaced from each other and the individual turns are spaced from each other to permit adequate air flow therebetween and thus to afford an extended heat-exchanging surface for indirectV heat-exchange between the air and the liquefied gas.

As best shown in FIG. 7, the end 121 of coil 119' is connected to a bushing 122, which is connected through a washer 123 to a coupling 124. A reducer bushingv125 is threaded into the coupling 124. A nipple 126 serves to connect a tubing 127 to the bushing 125. A similar con-V nection is aorded for the coil end 120.

The tubing 127 is connected to the outlet of a valve 123 carried on the manifold 112 and also, through a tubing 129', to the inlet of a valve 130 also carried on the manifold 112. Similarly, the coil end 120 is connected through a tubing 131 to the outlet of a valve 132 and, through a tubing 133, to the inlet of a valve 134, both valves being mounted on the manifold 112. The outlets of valves and 134 are connected to high-pressure gas outlet tube 13S, while the inlets of valves 128 and 132 are connected to high-pressure liquefied gas inlet tube 136.

By opening valves 12S and 134, liquefied gas will enter the coil 119 at end 121 and will travel toward end 120, being warmed and vaporized as it progresses. By the time the gas is discharged into the outlet tube 135 it should be only a few degrees below the ambient air temperature. A reverse direction fiow of gas can be provided by opening valves 130 and 132 instead Vof valves 128 and 134. The valves may conveniently be solenoid-operated under time or temperature control in order to aiford automatic transfer from each cycle portion to the next.

The apparatus illustrated in FIGS. 6 and 7 is of the same type as that illustrated in FIG. l in that it affords reversible fiow for both liquefied gas and air. This permits co-current flow during both cycle portions, which is the preferred mode of carrying out the invention.

In one embodiment of the apparatus shown in FIGS. 6 and 7, the air flow was approximately 3450 s.c.f.rn. The coil 119 was made of tubing having an outside diamv eter of 1/2 inch and a wall thickness of 0.082 inch. The coil length was 250 feet affording an exchanger surface area of approximately 33 square feet. The apparatus was used to charge a tank with gaseous oxygen. The liquid oxygen source included a pump which caused the delivered gas-to reach a pressure of 3000 p.s.i.g., the starting pressure with the gas tank empty being 0 p.s.i.g. With a half cycle (each cycle portion) time of approximately 30 minutes, the oxygen gas delivery was approximately 2000 s.c.f.h. The liquelied oxygen was delivered at approximately 297 F., while the gaseous oxygen was discharged from the exchanger at about 10 F. below ambient air temperature.

It is desirable that the air temperature not change appreciably in passing over the exchanger surface, since eiiiciency of operation will be maximized. By not appreciably is meant a temperature change of not more than about 10 F. Larger air temperature changes, for example, 50 F., can be accommodated, but at reduced efficiency.

It is particularly desirable that the invention be carried out so that during each cycle portion the ambient air Jdrst sweeps over the coldest area of the heat-exchanger surface and then over the area to be cleaned. In this way a maximum amount of the moisture in the air Willbe frozen out on the cold surface and the air will have a maximum capacity for picking up moisture from the warmer surface due to the concentration difference driving force, which to some extent is independent of temperaturc.

While the invention has been described in connection with specific steps, specific illustrations and specific uses, various modifications thereof will occur to those skilled in the art without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

l. A cyclic process for vaporizing and warming a liquefied gas having a boiling point below the temperature o-f `a gaseous heat source, comprising the steps of passing said liquefied gas over one face of an extended heat-exchanging surface of a heat-exchanger device, passing a relatively Warm gas from said heat source over the other face of said heat-exchanging surface in indirect heat-exchange with said liquefied gas to vaporize and warm the latter, permitting condensible -gases contained in said relatively warm gas from said heat source to freeze out on a first zone of said heat-exchanger surface which is the coldest zone during a first portion o-f each cycle, permitting condensible gases contained in said relatively Warm gas from said heat source to freeze out on a second zone of said heat-exchanger surface which is the coldest zone during a second portion of each cycle, u-tilizing said relatively warm gas from said heat source to evaporate previously -frozen out condensibles from said second zone during said first portion of each cycle, utilizing `said relatively warm gas from said heat source to evaporate previously frozen out condensibles from said first zone during said second portion of each cycle, and periodically reversing the direction of flow of said liquefied gas and said relatively warm gas to effect transfers between said first and second portions of cycle, said relatively warm gas during each portion of each cycle contacting first the coldest zone of said heat-exch-anger surface.

2. A cyclic process =for vaporizing and warming a liquefied gas having a boiling point below the Itemperature of available ambient air, comprising the steps of passing said liquefied gas over one face or" an extended heat-exchanging surface, of `a heat-exchanger device, passing ambient -air over the other face of said heatexchanging device in indirect heat-exchange with said liquefied gas to vaporize `and warm the latter, said air and said liquefied gas being passed along said surface in one direction during a first portion of each cycle and in the opposite direction during a second portion of each cycle whereby said air contacts first the coldest zone of said surface, permitting condensible ygases contained in said air to freeze out on the coldest zone of said surface during each portion of each cycle, utilizing said air during each portion of each cycle to evaporate condensible gases frozen out on the coldest zone of said surface during the preceding cycle portion, and peridicially reversing the direction of iiow of said liquefied gas and said air, the time duration of each portion of each cycle being selected so that the condensible gases frozen out on said exchanger surface during the preceding cycle portion are substantially completely evaporated.

3. The process set forth in claim 2, in which said liquefied Vgas is selected from the `group consisting of oxygen, nitrogen and argon.

4. The process set forth in claim 2, in which the time duration of each cycle portion is not ygreater than the time required .for the temperature of said vaporized and warmed `gas to 'fall below a predetermined value.

5. A cyclic process for vaporizing and Warming a liquefied gas having a boiling point below the temperature of available yambient air, comprising the steps of passing said liquefied gas over one face of an extended heat-exchanging surface of a heat exchanger device, passing ambient air over the other -face of said heat-exchanging surface in indirect heat-exchange with saidk liquefied lgas to vaporize and warm the latter, the relative mass flows and velocities of said liquefied gas and said air being selected so that the temperature of said air does not change appreciably during said heat-exchange, said air and said liquefied gas being passed along said surface in one direction during a first portion of each cycle and in the opposite direction during a second portion of each cycle whereby said air contacts first the coldest zone of said surface, permitting condensible gases contained in said iai-r to freeze out on the coldest zone of said surface during each portion of each cycle, utilizing said fair during each portion of each cycle to evaporate condensible gases frozen out on the coldest zone of said surface during the preceding cycle portion, and periodically reversing the direction of flow of said liquefied gas and -said air, the time duration of each portion o-f each cycle being selected so Ithat the condensible gases frozen out on said exchanger surface during the preceding cycle por-tion are substantially completely evaporated.

6. A cyclic process for vaporizing and warming a liqueed Vgas having a boiling point below the temperature of a ygaseous heat source, comprising the steps of passing said liquefied gas over one face -of an extended heat-exchanging surface of a heat-exchanger device, passing a relatively Warm gas from said heat source over the other face of said heat-exchanging surface in indirect heat-exchange with said liquefied gas to vaporize and Warm the latter, said liquefied gas and said relatively warm gas being passed along said surface in one direction during a first portion of each cycle and in the opposite direction during a second portion of each cycle whereby said relatively warm 'gas contacts first the coldest zone of said surface, permitting condensible gases contained in said relatively warm gas -to `freeze out on the coldest zone of said surface during each portion of each cycle, utilizing said relatively Warm gas during each portion of each cycle to evaporate condensible gases frozen out on the coldest zone of said surface during the preceding cycle portion, rand periodically reversing the direction of iiow of said liquefied gas and said relatively Warm gas, the time duration of each portion of each cycle being selected so that the condensible gases yfrozen out on said exchanger surface during the preceding cycle portion are substantially completely evaporated.

7. A cyclic process for vaporizing and warming a liquefied `gas having a boiling point below the temperature of available ambient air, comprising the steps of passing said Iliquefied gas over one face of each of two axially spaced axially extended heat-exchanging surfaces of a heat-exchanging device, said liquefied gas passing along said surfaces in opposite directions, passing ambient air over the other face o-f each of said heat-exchanging surfaces in indirect heat-exchange with said liquefied gas, said ambient air passing first along one of said surfaces and then along the other of said surfaces during a first portion of each cycle, said ambient air passing first along the other of said surfaces and then along said one surface during a second portion of each cycle, permitting condensible gases including Water vapor and carbon dioxide contained in said air to freeze out on said one surface during said first portion of each cycle and on said other surface during said second portion of each cycle, utilizing said air passing along said one surface during said second portion of eac-h cycle and along 'said other surface during said first portion of each cycle to evaporate from said surfaces condensible gases frozen out on said respective surfaces during the preceding cycle portion, and periodically reversing said direction of fiow of said air and said directions of flow of said liquefied gas Iso that the ambient air entering said heat-exchanger device at all times contacts first the coldest zone of said surfaces, the time duration of each cycle portion being not greater than the time required for the temperature of the discharged warmed and vaporized gas to fall below a predetermined value.

Irl.

8'. TheV process set forth in clainr 7, in which said lique-V fied gas is slected from the group consisting of oxygen, nitrogen and argon.

9. A cyclic process for vaporizing and warming a liquefied gas having a boiling point below the temperature of available ambient air, comprising the steps of passing saidiliquefied gas over one face of each of said two axially spaced axially extended heat-exchanging surfaces of a heat-exchanging device, said liquefied gas passing along said surfaces in opposite directions, passing ambient air over the other face of each of said heat-exchanging surfaces in indirect heat-exchange with said liquefied gas, said ambient air passing first along one of said surfaces and. then along the other of said surfaces during a rst portion of each cycle, said ambient air passing first along the other of said surfaces and then along said one surface during a second portion of each cycle, the relative mass flows and velocities of said liquefied gas and said air being selected so that the temperature of said air does not change appreciably during said heat-exchange, permitting condensible gases contained in said air to freeze out on said one surface during said first portion of each cycle and on said other surface during said second portion of each cycle, utilizing said air passing along said one surface during said second portion of each cycle and along said other surface during said first portion of each cycle to evaporate from said surfaces condensible gases frozen out on said respective surfaces during the preceding cycle portion, and periodically reversing said direction of flow of said air and said directions of flow of said liquefied gas so that the ambient air entering said heatexchanger device at all times contacts first the coldest zone of said surfaces, the time duration of each cycle portion being not greater than the time required for the temperature of the discharged warmed and vaporized gas to fall below a predetermined value.

l0. A cyclic process for vaporizing and warming a liquefied gas having a boiling point below the temperature of a gaseous heat source, comprising the steps of passing said liquefied gas over one face of each of two axially spaced axially extended heat-exchanging surfaces of a heat-exchanger device, said liquefied gas passing along said surfaces in opposite directions, passing a relatively warm gas from said heat source over the other face of each of said heat-exchanging surfaces in indirect heat-exchange with said liquefied gas, said relatively warm gas passing first along one of said surfaces and then along the other of said surfaces during a first portion of each cycle, said relatively warm gas passing first along the other of said surfaces and then along said one surface during a second'portion of each cycle, permitting condensible -gases contained in said relatively warm gas to freeze out on said one surface yduring said first portion of each cycle and on said other sur-face during said second portion of each cycle, utilizing said relatively warm gas passing along said one surface during said second portion of each cycle and along said other surface during said first portion of each cycle to evaporate from said surfaces condensible gases frozen out on said respective surfaces during the preceding cycle portion, and periodically reversing said direction of flow of said relatively warm gas and said directions of flow of said liquefied gas so that the relatively warm gas entering said heat-exchanger device at all times `contacts first the coldest zone of said surfaces, the time duration of each cycle portion being not greater than the time required for the temperature of the discharged warmed and vaporized gas to fall below a predetermined value.

l1. A cyclic process for vaporizing and warming a liquefied gas having a boiling point below the temperature of available ambient ai-r, comprising the steps of passing said liquefied Igas over one face of each of two axially extended heat-exchanging surfaces of a heat-exchanger device, said liquefied gas passing along said surfaces in'opposite directions, passing ambient air over the other faceiof each of said heat-exchanging surfaces in in direct heat-exchange with said liquefied gas, said surfaces being disposed in the same axial position but laterally spaced from each other with respect to the direction of air flow therealong, permitting fiow of said liquefied gases along one of said surfaces only during a first portion of each cycle and along the other of said surfaces only during a second portion of each cycle, causing the direction of flow of said air during each portion of each cycle to be the same as the 4direction of flow of said liquefied gas, permitting condensible gases contained in said air to freeze out on the surface past which liquefied gas is flowing during each portion of each cycle, and utilizing said air flowing along the surface past which liquefied gas is not flowing during each portion of each cycle to evaporate therefrom condensible gases frozen out thereon during the preceding cycle portion, the time duration of each cycle portion being not greater than the time required for the temperature of the discharged vaporized and warmed gas to fall below a predetermined value.

12. The process set forth in claim l1 in which said liquefied gas is selected from the group consisting of oxygen, nitrogen and argon.

13. A cyclic process for vaporizing and warming a liquefied gas having a 4boiling point below the temperature of available ambient air, comprising the steps of passing said-liquefied gas over the face of each of two axially extended heat-exchanging surfaces of a heat-exchanger device, said liquefied gas passing along said surfaces in opposite directions, passing ambient air over the other face of each of said heat-exchanging surfaces in indirect -heat-exchange with said liquefied gas, said surfaces being disposed in the same axial position but laterally spaced from each other with respect to the direction of air flow therealong, the relative mass flows and velocities of said liquefied gas `and said air lbeing selected so that the temperature of said air does not change appreciably dur ing said heat-exchange, permitting flow of said liquefied gases along one of said surfaces only during a first portion of each cycle and along the other of said surfaces only during a second portion of each cycle, causing the direction of flow of said air during each portion of each cycle to be 4the same as the direction of flow of said liquefied gas, permitting condensible gases contained in said air to freeze out on the surface past which liquefied gas is flowing during each portion of each cycle, and utilizing said air flowing along the surface past which liquefied gas is not fiowing during each portion of each cycle to evaporate therefrom condensible gases frozen out thereon during the preceding cycle portion, the time duration of each cycle portion being not greater than the time required -for the temperature of the discharged vaporized and warmed gas to fall below a predetermined value.

14. A cyclic process for vaporizing and warming a liquefied gas having a boiling point below the temperalture of a gaseous heat source, comprising the steps of passing said liquefied gas over one face of each of two axially extended heat-exchanging surfaces of a heat-exchanger device, said liquefied gas passing along said surfaces in opposite directions, passing a relatively Warm gas from said heat source over the other face of each of said heat-exchanging sur-faces in indirect heat-exchange with said liquefied gas, said surfaces being disposed in the same axial position but laterally spaced from each other with respect to the direction of relatively warm gas flow therealong, permitting flow of said liquefied gases along one of said surfaces only during a first portion of each cycle and along the other of said surfaces only during a second portion of each cycle, causing the direction of flow of said 4relatively Warm gas during each portion of each cycle to be the same as the direction of flow of said liquefied gas, permitting condensible gases contained in said relatively warm gas to freeze out on the surface past which liquefied gas is flowing during each portion of each cycle, and utilizing said relatively Warm gas fiowing along the surface past which liqueed gas is not flowing during each portion of each cycle to evaporate therefrom condensible gases frozen out thereon during the preceding cycle portion, the time .duration of each cycle portion being not greater than the time required for the temperature of the discharged vaporized and warmed gas to fall below a predetermined value.

2,445,705 Weinstein July 20, 1948 14 -Ringquist Sept. 6, Monroe Jan. 3, I-ue Sept. 18, Enger Feb. 18, Dorf May 6, Brandt Jan. 13, Siggelin May 5, IPalazzo etal Oct. 18,

FOREIGN PATENTS Australia June 28,

UNITED STATES PATENT OFFICE -CERTIFICATE OF CORRECTION Patent No., 3,053,317 October l6, l962 Laurel E. Putman f'wt is hereby certified that error appears in the above numbered patent requiring correction and that the seid Letters Patent should read as corrected below.

Column 3, line 19, for "pressure," read pressure, line 23, for "serve" read serves line 59, after "that" insert half line 63, for "are" read area column 6', line 75, for "sections" read section column 9, linesA 57 and 58, for "peridically read periodically column ll, line 7, strike out "said", second occurrence; line 9, for

"heat-exchanging" read heat-exchanger column l2, line 27, for "the" read one Signed and sealed this 5th day of March 1963.,

(SEAL) Attest:

DAVID L. LADD Commissioner of Patents ESTON Go JOHNSON Attesting Officer 

